THERE is an obvious need for a marker that will differentiate one type of lymphocyte from another. The need has become urgent in view of recent evidence suggesting that there are at least two populations of lymphocytes, one thymus-derived and one bone marrow-derived, which participate in different ways in the immune response1. The theta (θ) isoantigen (θ is determined by a single locus with two alleles: θAKR found in AKR and RF mice and θC3H present in most other inbred strains of mice tested), described by Reif and Allen2,3, which is found chiefly in thymus lymphocytes and brain, and to a lesser extent in peripheral lymphocytes in mice, seemed a possible antigenic marker of thymus-derived lymphocytes. To establish that θ is such a marker, it is necessary to demonstrate that there is a discrete population of peripheral lymphocytes which carry the antigen and that these cells are thymus-dependent.

Theta isoantigen as a marker of thymus-derived lymphocytes in mice (Reprinted from Nature vol 224, pg 378-379, 1969)

The staging of human embryos, as distinct from seriation, depends on a morphological scheme devised by Streeter and completed by O'Rahilly, who proposed the term Carnegie stages. To avoid misconceptions and errors, and to place new findings in perspective, it is necessary to summarize the essentials of the Carnegie system: (1) Twenty-three stages cover the embryonic period, i. e. the first 8 postfertilizational weeks of development. (2) The system is based on internal as well as external features, and the use of only external criteria is subject to serious limitations. For example, precise delineation of stages 19-23 and of the embryonic-fetal transition depends on histological examination. (3) Prenatal measurements are not an integral component of the staging system, and hence a stage should never be assigned merely on the basis of embryonic length. A 20-mm embryo, for example, could belong to any of three stages. Measurements, however, are important for the assessment of age, and very few measurements are available for staged embryos. Presented here and based on accurate staging are the maximum diameter of the chorionic sac, the crown-heel length, the greatest length exclusive of the lower limbs, the biparietal diameter, the head circumference, the length of the hindbrain, the total length of the brain, and the lengths of the limbs as well as of their segments, including the foot length. (4) Prenatal ages are also not an integral part of the staging system and hence a stage should never be assigned merely on the basis of prenatal age. Ages, however, are of clinical importance and their estimate has been rendered more precise by accurate timing of fertilization followed by ultrasonography. Prenatal age is postfertilizational and hence some 2 weeks less than the postmenstrual interval. The term gestational age is ambiguous and should be discarded. Presented here is a new graph showing proposed estimates of age in relation to stages and based on current information.

Developmental stages in human embryos: revised and new measurements.

Objective To assist clinicians in assigning gestational age based on ultrasound biometry. Outcomes To determine whether ultrasound dating provides more accurate gestational age assessment than menstrual dating with or without the use of ultrasound. To provide maternity health care providers and researchers with evidence-based guidelines for the assignment of gestational age. To determine which ultrasound biometric parameters are superior when gestational age is uncertain. To determine whether ultrasound gestational age assessment is cost effective. Evidence Published literature was retrieved through searches of PubMed or MEDLINE and The Cochrane Library in 2013 using appropriate controlled vocabulary and key words (gestational age, ultrasound biometry, ultrasound dating). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies written in English. There were no date restrictions. Searches were updated on a regular basis and incorporated in the guideline to July 31, 2013. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies. Values The quality of evidence in this document was rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care (Table 1). Benefits, harms, and costs Accurate assignment of gestational age may reduce post-dates labour induction and may improve obstetric care through allowing the optimal timing of necessary interventions and the avoidance of unnecessary ones. More accurate dating allows for optimal performance of prenatal screening tests for aneuploidy. A national algorithm for the assignment of gestational age may reduce practice variations across Canada for clinicians and researchers. Potential harms include the possible reassignment of dates when significant fetal pathology (such as fetal growth restriction or macrosomia) result in a discrepancy between ultrasound biometric and clinical gestational age. Such reassignment may lead to the omission of appropriate—or the performance of inappropriate—fetal interventions.

https://www.jogc.com/article/S1701-2163(15)30664-2/pdf

Determination of Gestational Age by Ultrasound

Cytokeratin 20 Is a General Marker of Cutaneous Merkel Cells While Certain Neuronal Proteins Are Absent

In this article, we record the history of obstetric ultrasound as it developed worldwide in the second half of the twentieth century. The technological advances during this period saw the evolution of equipment from the original adapted metal flaw detectors producing a simple A-scan to the modern, purpose built, real-time colour flow machines with three-dimensional capability (Fig. 1). Clinically, ultrasound began as a research tool, but the poor quality of the images led to the ridicule of many of the early investigators. However, because of their perseverance, ultrasound developed into an imaging modality providing immense diagnostic capabilities and facilitating with precision many invasive procedures, diagnostic and therapeutic, both of which have made significant contributions to patient care. In this history, we recall the people, the personalities, and the problems they encountered during the development of ultrasound and how these problems were resolved, so that ultrasound now is available for use in the care of pregnant women throughout the developed world.

“forthee....towhom% nosoundisdissonantwhichtellsoflife”% —coleridge

Fetal foot length as a predictor of gestational age

Surface receptors and immune activity of purified human circulating mononuclear cells: IV. The demonstration of seven subclasses of T cells in the circulation of the normal individual: The cytotoxic activities of these cells

Surface receptors and immune activity of purified human circulating mononuclear cells. I. The effects of lysis of the sheep red blood cells (SRBC) in the T-cell rosettes on the receptors and cytotoxic activities of the T cells. T cells with receptors for complement.

Suzi Sklar

Papers

Fetal foot length as a predictor of gestational age

Surface receptors and immune activity of purified human circulating mononuclear cells: IV. The demonstration of seven subclasses of T cells in the circulation of the normal individual: The cytotoxic activities of these cells

Surface receptors and immune activity of purified human circulating mononuclear cells. I. The effects of lysis of the sheep red blood cells (SRBC) in the T-cell rosettes on the receptors and cytotoxic activities of the T cells. T cells with receptors for complement.